Monthly Archives: August 2015

So many dimples! One wing ready for riveting!

Well, I got to work finishing the top wing skins (Section 16-02).  It took a while to strip off the blue plastic (14 ribs x 2 wings plus 3 horizontal stripes).  I finally got that done and finished the countersinks for the wing walks.  My wife came by for lunch (and to keep me from spending all day with the plane — she’s a bit jealous and calls the plane, my “mistress“).  She took a picture so the FAA will know that it was me sweating over these skins in the garage.

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Doing the countersinks for the wing walk doublers… the instructions caution to make sure these don’t go too deep.  The skin is right on the borderline of too thin to countersink, but it works better to deal with the top skin/doubler/rib sandwich.

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Next, I had to pull the skins off to make a scarf joint along the forward edge of the skins.  I’m starting with the right wing.  It’s easier to leave the skins on the rib skeleton as I have no better place to store them.

I found the illustration very confusing.  The shape on the bottom does not nest with the shape on the top.  It took me a while, but I finally figured out that they just wanted the two skins to lay flat on the spar.  Once I saw that, it was easier to figure out how to shape the corner.

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The inner top skin sits underneath the outer top skin.  The gap between the spar and outer top skin is too big if you just let it overlap.  So, we file and sand and polish a bit off the inner skin and then remove a matching amount off the outer skin and try for a flat joint.

I clecoed my skins to the tables to get them lined up and then filed and sanded the corners.  I used my bastard file since you have to carefully remove a surprising large amount of material.  Still had to be careful.  Several bloggers reported removing too much and having damaged or rounded corners.  I used some sandpaper and a paint stir stick to finish it off.

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The joint is a lot flatter after the adding the scarf — not sure this picture does it justice.

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There is a lot of dimpling to do on the skins.  The inner skin has almost 250 dimples to make (in addition to the 70-80 countersinks).  The outer skin has over 450!  My son dropped by (for lunch) and I enlisted his help in doing the dimpling on the DRDT-2.  It can reach all the dimples and it made nice crisp ones.

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The blue X’s are reminders not to dimple the wing tip attach holes quite yet.

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The two foot throat can reach all the way to the middle of the skin.  2015-08-09 15.25.18

With the dimpling done, it was time to prime the skins.  I ran a line of primer over the rivet lines and filled in with a light coat of primer.  You can see the large outer skin, the smaller inner skin, and the two wing walk doublers (those are primed on both sides).

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I also needed to finish the J-stiffeners that go down the middle of the wing.  These were match drilled in the very first wing task a few months ago.  I stripped off the blue plastic, and ran a deburring bit through the holes.  Then they got shot with some primer.  They’re not in the wing yet, but that should not take long on the next build day.

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So, the wing is just about ready to rivet.  With the dimples in place, the wing really feels solid.  It’s amazing how much just dimpling adds to the sheer resistance for the skins.  They really lock in tight!2015-08-09 17.44.16

I also had one last minute task on the right wing.  One of my rib flange holes was a bit enlarged when I double clutched the dimpler.  I reamed this out to 1/8″ (hence the copper cleco) and marked it for an “oops” rivet.  The tape goes over the cleco depressor, so I’ll be sure to remember to swap in the NAS 1097 rivet for this one hole.  The head is a normal 3/32″ size, so it won’t be noticeable.

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Next, I have to slide the J-stiffeners into the right wing and then do all the dimple and prep work for the left wing skins.  Then, it will just be a lot of riveting to finish this section.

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Rear spar finally done… Wing skins on for the first time

I had 192 rivets left in the rear wing spar…. I finally got them all!  I did most of them while the spar was still loosely attached to the ribs.  This gave me a nice clamping surface to hold the spar steady for the riveting.  Most of the double plates were easy to get at with my longeron yoke (switching sides as needed).  My pneumatic squeezer is pretty wimpy on the 1/8″ rivets, so all of these were hand squeezed.  I picked one rivet size and got all the rivets that matched that size.  Here, I get the AN470AD-4.5 rivets to hold the aileron bracket in place.

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The inner doubler plate is really thick.  It uses AN470-AD-6’s on the fork part…

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… and massively long AN470-AD-8’s on the second doubler plate.  I switched to my basic yoke for those to get more reach.

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That finished the spar riveting.   Here it is with the orange tape I used to keep from riveting the rib attached points still in place.

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There is one more step left before attaching the spar to the ribs.  There is a rather dire looking note in step 6 that warns that the spar attach hole must be reamed on a drill press.

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I moved my tabletop drill press over on to my work bench and propped the spar up to make it level.  The hole was already at 11/32″, so reaming it to 3/8″ did not remove a lot of meta. (NOTE: a reamer would work better here than a bit.  I thought I ordered a new reamer but, in fact got a bit…. You should order a .311 and .375 reamer. You’ll need then for the fuselage anyway)

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I still had to rivet the spars to the ribs.  Since I could not push individual ribs out of the way anymore, it was harder to get the yoke into the tight corners.  I ended up bucking two of the AD426 rivets here.  Not a big deal.  It settled down very flush.

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I was able to reach the rest of the ribs with my 4″ flat nose yoke.2015-08-01 13.09.47 2015-08-01 15.18.32

Just like that!  I had some wing skeletons!  Section 15 done!.  They were a lot less floppy once I got everything riveted, but they didn’t seem very strong.  That was about to change.

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Time to start section 16.  The Top Wing Skins! I dug down to the very bottom of the crate and pulled out the inboard and outboard top skins.  My son and a couple of his friends stopped by.  They had a lot of fun clecoing the right wing!  Once the skins went on, the wings tightened up right away.  They feel very solid (and are getting heavy!).  I’m sure they will really pull it tight once I rivet.

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My son and his friends got bored and left after a while.  I did the left wing on my own.  I used a pin punch to help me line up the ribs (or used a step ladder to reach down inside and move the rib into position).

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The prepunched holes are amazing.  Every hole in the skin lined right up with a rib flange. My father-in-law told me horrifying tales of rivet fan spacing lines on skins and carefully blue lining the rib flanges.  Then, the ribs where nudged into place until the blue showed through the hole and drilled.  It was quite tedious!

The whole cleco action on this kit took me about an hour, tops.  Most of the holes are already final drilled to size.  I just need to dimple.  Very happy to be doing it this way.

Well, most of the holes are final.  You need to final drill through the doubler plates.  I snuck over to the workshop early Sunday morning and reamed them out before church!

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You also need to match drill and final drill some of the nut plate holes.  That went pretty fast as well.  The blue mark is to remind me where the #19 holes for the nut plate go.  My wings were upside down relative to the plans, so I was extra careful

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Where the skin hangs out past the rear spar (out where the gap farings go), you need to dimple one hole for a #8 screw head.  Again, the plans have dire warnings urging caution.

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I carefully smoothed the hole with a deburring bit, a hole deburring tool, and a rolled up piece of sandpaper.  They were very smooth by that point.  I carefully squeezed the dimple.  They both came out very clean.

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The next step is to gently countersink the wing skin over the doubler skins.  The skins are pretty thin for countersinking, but with the doubler plate underneath and the undimpled rib flanges below, that’s what the plans call for.  There is yet another dire note telling you it is better to be shallow than to be deep on the countersinks (up to 0.005″ shallow).  I wanted to start on that task fresh next week, so I just stripped off some of the blue plastic to get good access to the holes I need to countersink.

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Next week, I’ll countersink the wing walk holes, do some skin fitting (the corner where the inboard and outboard skins meet the tank skins gets shaped to make a smooth edge), and get some dimpling done.  I’ll probably get to riveting in two weeks.   There are a lot of rivets!  I’ll do it with my back rivet bucking bar and a 12″ back rivet tool.  This should give me a very clean top surface.